Apparatus and method for controlling operation of compressor

ABSTRACT

An apparatus for controlling a compressor includes a stroke calculator for calculating a stroke estimate value of a compressor based on a value of a current applied to a motor of the compressor and a value of a voltage applied to the motor of the compressor; an operation frequency reference determining unit for integrating the stroke estimate value to output an integrated stroke value, detecting a mechanical resonance frequency of the compressor based on the integrated stroke estimate value and the current value, and determining the detected mechanical resonance frequency as an operation frequency reference value; and a controller for varying a current operation frequency of the compressor according to the determined operation frequency reference value.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compressor and, more particularly, toan apparatus and method for controlling an operation of a reciprocatingcompressor.

2. Description of the Prior Art

In general, a reciprocating compressor does not employ a crank shaft forconverting a rotational motion into a linear motion, so it has highercompression efficiency than a general compressor.

When the reciprocating compressor is used for a refrigerator or anair-conditioner, a compression ratio of the reciprocating compressor canbe varied by varying a stroke voltage inputted to the reciprocatingcompressor in order to control cooling capacity.

A conventional reciprocating compressor will now be described withreference to FIG. 1.

FIG. 1 is a block diagram showing the construction of an apparatus forcontrolling an operation of a reciprocating compressor in accordancewith a prior art.

As shown in FIG. 1, a conventional apparatus for controlling anoperation of a reciprocating compressor includes: a current detector 4for detecting a current applied to a motor (not shown) of areciprocating compressor 6; a voltage detector 3 for detecting a voltageapplied to the motor; a stroke calculator 5 for calculating a strokeestimate value of the compressor based on the detected current andvoltage values and a parameter of the motor; a comparator 1 forcomparing the calculated stroke estimate value and a pre-set strokereference value and outputting a different value according to thecomparison result; and a stroke controller 2 for controlling anoperation (stroke) of the compressor 6 by varying a voltage applied tothe motor according to the difference value.

The apparatus for controlling an operation of the reciprocatingcompressor operates as follows.

First, the current detector 4 detects a current applied to the motor ofthe compressor 6 and outputs the detected current value to the strokecalculator 5. At this time, the voltage detector 3 detects a voltageapplied to the motor and outputs the detected voltage value to thestroke calculator 5.

The stroke calculator 5 calculates a stroke estimate value (X) of thecompressor by substituting the detected current and voltage values and aparameter of the motor to equation (1) shown below and applies theobtained stroke estimate value (X) to the comparator 1.

$\begin{matrix}{X = {\frac{1}{\alpha}{\int{\left( {V_{M} - {Ri} - {L\overset{\_}{i}}} \right){\mathbb{d}t}}}}} & (1)\end{matrix}$wherein ‘R’ is a motor resistance value, ‘L’ is a motor inductancevalue, α is a motor constant value, V_(M) is a value of a voltageapplied to the motor, ‘i’ is a value of a current applied to the motor,and ‘ī’ is a time change rate of the current applied to the motor.Namely, ‘ī’ is a differentiated value of ‘i’ (di/dt).

The comparator 1 compares the stroke estimate value with the strokereference value and applies a difference value according to thecomparison result to the stroke controller 2.

The stroke controller 2 controls the stroke of the compressor 6 byvarying a voltage applied to the motor of the compressor 6 based on thedifference value. This will be described with reference to FIG. 2.

FIG. 2 is a flow chart of a method for controlling an operation of thereciprocating compressor in accordance with the prior art.

First, when the stroke calculate 5 applies the stroke estimate value tothe comparator 1 (step S1), the comparator 1 compares the strokeestimate value with the pre-set stroke reference value (step S2) andoutputs a difference value according to the comparison result to thestroke controller 2.

If the stroke estimate value is smaller than the stroke reference value,the stroke controller 2 increases a voltage applied to the motor tocontrol the stroke of the compressor (step S3). If, however, the strokeestimate value is greater than the stroke reference value, the strokecontroller 2 reduces the voltage applied to the motor (step S4).

Thus, in the conventional apparatus and method for controlling anoperation of the reciprocating compressor, even though a mechanicalresonance frequency of the compressor is varied because of the change inthe voltage applied to the motor of the compressor based on the strokeestimate value an the stroke reference value, the reciprocatingcompressor is operated with the always same operation frequency, causinga problem that operation efficiency of the reciprocating compressordeteriorates.

A reciprocating compressor in accordance with a different embodiment ofthe present invention is disclosed in U.S. Pat. No. 6,644,943 registeredon Nov. 11, 2003.

SUMMARY OF THE INVENTION

Therefore, an object of the present invention is to provide an apparatusand method for controlling an operation of a compressor capable ofenhancing operation efficiency of a compressor even though a load of thecompressor is changed.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described herein,there is provided an apparatus for controlling a compressor including: astroke calculator for calculating a stroke estimate value of acompressor based on a value of a current applied to a motor of thecompressor and a value of a voltage applied to the motor of thecompressor; an operation frequency reference determining unit forintegrating the stroke estimate value to output an integrated strokevalue, detecting a mechanical resonance frequency of the compressorbased on the integrated stroke estimate value and the current value, anddetermining the detected mechanical resonance frequency as an operationfrequency reference value; and a controller for varying a currentoperation frequency of the compressor according to the determinedoperation frequency reference value.

To achieve the above object, there is also provided an apparatus forcontrolling an operation of a compressor including: a current detectorfor detecting a current applied to a motor of a compressor; a voltagedetector for detecting a voltage applied to the motor; a strokecalculator for calculating a stroke estimate value of the compressorbased on the detected current and voltage values and a parameter of themotor; an operation frequency reference value determining unit forintegrating the stroke estimate value to output an integrated strokevalue, detecting a mechanical resonance frequency of the compressorbased on the integrated stroke estimate value and the detected currentvalue, and determining the detected mechanical resonance frequency as anoperation frequency reference value; a comparator for comparing thestroke estimate value outputted from the stroke calculator with a strokereference value and outputting a difference value according to thecomparison result; and a controller for controlling an operation of thecompressor by varying a current operation frequency according to thedetermined operation frequency reference value and varying the voltageapplied to the motor of the compressor according to the difference valueoutputted from the comparator.

To achieve the above object, there is also provided a method forcontrolling an operation of a compressor including: integrating a strokeestimate value of a compressor based on a value of a current applied toa motor of a compressor and a voltage applied to the motor andoutputting an integrated stroke value; detecting a mechanical resonancefrequency of the compressor based on the integrated stroke value and thecurrent value; determining the mechanical resonance frequency as anoperation frequency reference value of the compressor; and varying acurrent operation frequency of a compressor according to the determinedoperation frequency reference value.

To achieve the above object, there is also provided an apparatus forcontrolling an operation of a compressor including: a stroke calculatorfor calculating a stroke estimate value of a compressor based on a valueof a current applied to a motor of the compressor and a value of avoltage applied to the motor of the compressor; an operation frequencyreference value determining unit for integrating the current value tooutput an integrated current value, detecting a mechanical resonancefrequency of the compressor based on the stroke estimate value and theintegrated current value, and determining the detected mechanicalresonance frequency as an operation frequency reference value; and acontroller for varying a current operation frequency of the compressorbased on the determining the operation frequency reference value.

To achieve the above object, there is also provided an apparatus forcontrolling an operation of a compressor including: a current detectorfor detecting a current applied to a motor of a compressor; a voltagedetector for detecting a voltage applied to the motor; a strokecalculator for calculating a stroke estimate value of the compressorbased on the detected current and voltage values and a parameter of themotor; an operation frequency reference value determining unit forintegrating the current value to output an integrated current value,detecting a mechanical resonance frequency of the compressor based onthe stroke estimate value and the integrated current value, anddetermining the detected mechanical resonance frequency as an operationfrequency reference value; a comparator for comparing the strokeestimate value outputted from the stroke calculator with a strokereference value and outputting a difference value according to thecomparison result; and a controller for controlling an operation of thecompressor by varying a current operation frequency according to thedetermined operation frequency reference value and varying the voltageapplied to the motor of the compressor according to the difference valueoutputted from the comparator.

To achieve the above object, there is also provided a method forcontrolling an operation of a compressor including: calculating a strokeestimate value of a compressor based on a value of a current applied toa motor of the compressor and a value of a voltage applied to the motor;integrating the current value to output an integrated current value;detecting a mechanical resonance frequency of the compressor based onthe stroke estimate value and the integrated current value; determiningthe mechanical resonance frequency as an operation frequency referencevalue of the compressor; and varying a current operation frequency ofthe compressor according to the determined operation frequency referencevalue.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

In the drawings:

FIG. 1 is a block diagram showing the construction of an apparatus forcontrolling an operation of a reciprocating compressor in accordancewith a prior art;

FIG. 2 is a flow chart of a method for controlling an operation of thereciprocating compressor in accordance with the prior art;

FIG. 3 is a block diagram showing the construction of an apparatus forcontrolling an operation of a compressor in accordance with a firstembodiment of the present invention;

FIGS. 4A and 4B are graphs showing a phase of a current applied to amotor of the compressor and a phase of a stroke of the compressor inaccordance with the first embodiment of the present invention;

FIG. 5 is a flow chart of a method for controlling an operation of thecompressor in accordance with the first embodiment of the presentinvention;

FIG. 6 is a block diagram showing an apparatus for controlling anoperation of a compressor in accordance with a second embodiment of thepresent invention;

FIG. 7 is a graph showing a phase of a current applied to a motor of thecompressor and a phase of a stroke of the compressor in accordance withthe second embodiment of the present invention; and

FIG. 8 is a flow chart of a method for controlling an operation of thecompressor in accordance with the second embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An apparatus and method for controlling an operation of a compressorcapable of enhancing operation efficiency of a compressor although aload of the compressor is varied in accordance with preferredembodiments of the present invention will now be described withreference to FIGS. 3 to 8.

FIG. 3 is a block diagram showing the construction of an apparatus forcontrolling an operation of a compressor in accordance with a firstembodiment of the present invention.

As shown in FIG. 3, an apparatus for controlling an operation of acompressor includes: a current detector 40 for detecting a currentapplied to a motor of a compressor 60; a voltage detector 30 fordetecting a voltage applied to the motor of the compressor 60; a strokecalculator 50 for calculating a stroke estimate value of the compressor60 based on the detected current and voltage values and a parameter ofthe motor; an operation frequency reference value determining unit 70for integrating the stroke estimate value, detecting a mechanicalresonance frequency of the compressor based on the integrated strokeestimate value and the detected current value, and determining thedetected mechanical resonance frequency as an operation frequencyreference value; a comparator 10 for comparing the stroke estimate valueoutputted from the stroke calculator 50 with a stroke reference valueand outputting a difference value according to the comparison result;and a controller 20 for controlling an operation of the compressor 60 byvarying a current operation frequency according to the determinedoperation frequency reference value and varying the voltage applied tothe motor of the compressor 60 according to the difference valueoutputted from the comparator 10.

The operation of the apparatus for controlling an operation of thecompressor in accordance with the preferred embodiment of the presentinvention will be described in detail as follows.

First, the current detector 10 detects a current applied to thecompressor 60 and outputs the detected current value to the strokecalculator 50 and the operation frequency reference value determiningunit 70. At this time, the voltage detector 30 detects a voltage appliedto the compressor 60 and outputs the detected voltage value to thestroke calculator 50.

The stroke calculator 50 calculates a stroke estimate value of thecompressor 60 based on the current value outputted from the currentdetector 40, the voltage value outputted from the voltage detector 30and a pre-set motor parameter, and then outputs the calculated strokeestimate value to the comparator 10 and the operation frequencyreference value determining unit 70.

The comparator 10 compares the stroke reference value with the strokeestimate value outputted from the stroke calculator 50 and then outputsa difference value according to the comparison result to the controller20.

The controller 20 controls an operation of the compressor 60 by varyingthe voltage applied to the compressor 60 according to the differencevalue outputted from the comparator 10.

The operation frequency reference value determining unit 70 integratesthe stroke estimate value, detects a mechanical resonance frequency ofthe compressor based on the integrated stroke estimate value and thecurrent value detected by the current detector 40, and determines thedetected mechanical resonance frequency as an operation frequencyreference value.

For example, the operation frequency reference value determining unit 70multiplies integrated stroke values and detected current values duringone period when the motor is in a resonant state and determines anoperation frequency detected when the sum of the multiplied valuesbecomes zero (0) as an operation frequency reference value. In otherwords, the operation frequency reference value determining unit 70recognizes an operation frequency detected when the sum of valuesobtained by multiplying the integrated stroke values and the detectedcurrent values is 0, as a mechanical resonance frequency and determinesthe mechanical resonance frequency as the operation frequency referencevalue. Herein, when the operation frequency and the mechanical resonancefrequency are identical, operation efficiency of the compressor isenhanced.

The mechanical resonance frequency value is calculated through equation(2) shown below:Σ(∫Xdt×i)  (2)

Namely, the operation frequency reference value determining unit 70recognizes the operation frequency detected when the value calculatedthrough equation (2) is 0 as the mechanical resonance frequency anddetermines the mechanical resonance frequency as the operation frequencyreference value. Herein, ‘X’ is a stroke estimate value and ‘i’ is avalue of a current applied to the motor.

Thereafter, the controller 20 controls an operation of the compressor 60by varying a current operation frequency of the compressor 60 accordingto the operation frequency reference value outputted from the operationfrequency reference value determining unit 70. That is, if the operationfrequency reference value is greater than the current operationfrequency value, the controller 20 increases the current operationfrequency. If the operation frequency reference value is smaller thanthe current operation frequency value, the controller 20 reduces thecurrent operation frequency.

A stroke phase and a current phase of the compressor will be describedwith reference to FIGS. 4A and 4B.

FIGS. 4A and 4B are graphs showing a phase of a current applied to amotor of the compressor and a phase of a stroke of the compressor inaccordance with the first embodiment of the present invention, in whichthe stroke means a position of a piston when the piston of thecompressor makes a reciprocal movement and the stroke phase means awaveform (sine wave) according to a position of the piston when thepiston makes the reciprocal movement.

As shown in FIG. 4A, a stroke phase and a current phase have thedifference of 90°, and in this respect, experimentation reveals thatwhen the stroke phase and the current phase have the difference of 90°,even if a load of the compressor is changed, a resonance phenomenonoccurs.

FIG. 4B shows a phase obtained by integrating the stroke phase of FIG.4A and the current phase.

As shown in FIG. 4B, experimentation reveals that even though the loadof the compressor, if the sum of values obtained by multiplying theintegrated stroke values and the values of the current applied to themotor is 0, the resonance phenomenon occurs. That is, the integratedstroke values and current values during one period are multiplied whenthe motor is in the resonant state and then when the multiplied valuesare added, the added value becomes 0. Accordingly, the operationfrequency detected when the sum of values obtained by multiplying thecurrent values and the integrated stroke values is 0, is the same as themechanical resonance frequency.

The operation of the operation frequency reference value determiningunit 70 of multiplying the integrated stroke values and the currentvalues during one period, adding the multiplied values, detecting theoperation frequency when the sum is 0, and determining the detectedoperation frequency value as an operation frequency reference value willbe described with reference to FIG. 5 as follows.

FIG. 5 is a flow chart of a method for controlling an operation of thecompressor in accordance with the first embodiment of the presentinvention.

As shown in FIG. 5, a method for controlling an operation of thecompressor in accordance with the first embodiment of the presentinvention includes: detecting values of a current and voltage applied tothe compressor 60; calculating a stroke estimate value of the compressorbased on the current and voltage values; integrating the stroke estimatevalue to output an integrated stroke estimate value; detecting amechanical resonance frequency of the compressor based on the sum ofvalues obtained by multiplying the integrated stroke estimate values andthe current values during one period and determining the mechanicalresonance frequency as an operation frequency reference value; andvarying a current operation frequency of the compressor according to thedetermined operation frequency reference value.

Herein, the operation frequency detected when the sum of values obtainedby multiplying the integrated stroke estimate values and the current isvalues during one period is 0 is the same as the mechanical resonancefrequency of the compressor. Accordingly, when the current operationfrequency of the compressor is varied according to the operationfrequency detected when the sum of values obtained by multiplying theintegrated stroke estimate values and the current values during oneperiod is 0, since the varied operation frequency is the same as themechanical resonance frequency, the operation efficiency of thecompressor can be enhanced.

First, the operation frequency reference value determining unit 70multiples the integrated stroke estimate values and the current valuesduring one period, adds the multiplied values (step S11), and thencompares the calculated sum with the sum of values obtained bymultiplying integrated stroke values and current values during aprevious one period (step S12).

If the sum of the values obtained by multiplying the integrated strokevalues and the current values during one period is greater than the sumof values obtained by multiplying the integrated stroke estimate valuesand the current values during a previous one period and the currentoperation frequency of the compressor 60 is greater than a previousoperation frequency (step S13), the operation frequency reference valuedetermining unit 70 continuously reduces the current operationfrequency, and then, determines an operation frequency (identical to themechanical resonance frequency) detected when the sum of the valuesobtained by multiplying the integrated stroke estimate values and thecurrent values during one period becomes 0, as an operation frequencyreference value (step S15).

If the sum of values obtained by multiplying integrated stroke estimatevalues and the current values is greater than the sum of values obtainedby multiplying the integrated stroke estimate values and the currentvalues during the previous period and if the current operation frequencyis smaller than a previous operation frequency (step S13), the operationfrequency reference value determining unit 70 continuously increases thecurrent operation frequency, and then, determines an operation frequencydetected when the sum of values obtained by multiplying the integratedstroke estimate values and the current values during the current oneperiod is 0 as an operation frequency reference value (step S16).

If the sum of values obtained by multiplying integrated stroke estimatevalues and the current values is smaller than the sum of values obtainedby multiplying the integrated stroke estimate values and the currentvalues during the previous period and if the current operation frequencyis smaller than a previous operation frequency (step S14), the operationfrequency reference value determining unit 70 continuously reduces thecurrent operation frequency, and then, determines an operation frequencydetected when the sum of values obtained by multiplying the integratedstroke estimate values and the current values during the current oneperiod is 0 as an operation frequency reference value (step S17).

Meanwhile, if the sum of values obtained by multiplying integratedstroke estimate values and the current values is smaller than the sum ofvalues obtained by multiplying the integrated stroke estimate values andthe current values during the previous period and if the currentoperation frequency is greater than a previous operation frequency (stepS13), the operation frequency reference value determining unit 70continuously increases the current operation frequency, and then,determines an operation frequency detected when the sum of valuesobtained by multiplying the integrated stroke estimate values and thecurrent values during the current one period is 0 as an operationfrequency reference value (step S18).

Accordingly, since the operation frequency detected when the sum ofvalues obtained by multiplying the integrated stroke estimate values andthe current values during one period is 0 is the same as the mechanicalresonance frequency of the compressor, the operation efficiency of thecompressor can be enhanced by varying the current operation frequencyaccording to the operation frequency detected when the sum of valuesobtained by multiplying the integrated stroke estimate values and thecurrent values during one period is 0.

In other words, while the reciprocating compressor is operating,whenever a load of the compressor is varied, a mechanical resonancefrequency of the compressor is detected based on the integrated strokeestimate values and the current values during one period, and then, theoperation frequency of the compressor is varied according to thedetected mechanical resonance frequency, thereby enhancing the operationefficiency of the compressor.

On the other hand, in the present invention, after the current appliedto the motor is integrated, the mechanical resonance frequency of thecompressor can be detected based on the integrated current value and thestroke estimate value.

Accordingly, the second embodiment of the present invention capable ofenhancing operation efficiency of the compressor by detecting themechanical resonance frequency of the compressor based on the integratedcurrent value and the stroke estimate value and varying the operationfrequency of the compressor according to the detected mechanicalresonance frequency, will now be described with reference to FIGS. 6 to8.

The construction of the apparatus for controlling an operation of thecompressor in accordance with the second embodiment of the presentinvention is the same as the first embodiment except for an operationfrequency reference value determining unit 100, and thus, the samereference numerals are give to the same elements.

FIG. 6 is a block diagram showing an apparatus for controlling anoperation of a compressor in accordance with a second embodiment of thepresent invention.

As shown in FIG. 6, the apparatus for controlling an operation of thereciprocating compressor in accordance with the second embodiment of thepresent invention includes: a current detector 40 for detecting acurrent applied to a motor of a compressor 60; a voltage detector 30 fordetecting a voltage applied to the motor of the compressor 60; a strokecalculator 50 for calculating a stroke estimate value of the compressor60 based on the detected current and voltage values and a parameter ofthe motor; an operation frequency reference value determining unit 100for integrating the detected current value, detecting a mechanicalresonance frequency of the compressor based on the integrated currentvalue and the detected stroke estimate value, and determining thedetected mechanical resonance frequency as an operation frequencyreference value; a comparator 10 for comparing the stroke estimate valueoutputted from the stroke calculator 50 with a stroke reference valueand outputting a difference value according to the comparison result;and a controller 20 for controlling an operation of the compressor 60 byvarying a current operation frequency according to the determinedoperation frequency reference value and varying the voltage applied tothe motor of the compressor 60 according to the difference valueoutputted from the comparator 10.

The operation of the apparatus for controlling an operation of thecompressor in accordance with the second embodiment of the presentinvention will be described in detail as follows.

First, the current detector 10 detects a current applied to thecompressor 60 and outputs the detected current value to the strokecalculator 50 and the operation frequency reference value determiningunit 100. At this time, the voltage detector 30 detects a voltageapplied to the compressor 60 and outputs the detected voltage value tothe stroke calculator 50.

The stroke calculator 50 calculates a stroke estimate value of thecompressor 60 based on the current value outputted from the currentdetector 40, the voltage value outputted from the voltage detector 30and a pre-set motor parameter, and then outputs the calculated strokeestimate value to the comparator 10 and the operation frequencyreference value determining unit 100.

The comparator 10 compares the stroke reference value with the strokeestimate value outputted from the stroke calculator 50 and then outputsa difference value according to the comparison result to the controller20.

The controller 20 controls an operation of the compressor 60 by varyingthe voltage applied to the compressor 60 according to the differencevalue outputted from the comparator 10.

The operation frequency reference value determining unit 100 integratesthe detected current value, detects a mechanical resonance frequency ofthe compressor based on the integrated current value and the strokeestimate value, and determines the detected mechanical resonancefrequency as an operation frequency reference value.

For example, the operation frequency reference value determining unit100 multiplies integrated current values and stroke estimate valuesduring one period when the motor is in a resonant state and determinesan operation frequency detected when the sum of the multiplied valuesbecomes the maximum as an operation frequency reference value. In otherwords, the operation frequency reference value determining unit 100recognizes an operation frequency detected when the sum of valuesobtained by multiplying the integrated current values and the strokeestimate values becomes the maximum, as a mechanical resonance frequencyand determines the mechanical resonance frequency as the operationfrequency reference value. Herein, when the operation frequency and themechanical resonance frequency are the same, operation efficiency of thecompressor is enhanced.

The mechanical resonance frequency value is calculated through equation(3) shown below:Σ(X×∫idt)  (3)

Namely, the operation frequency reference value determining unit 100recognizes the operation frequency detected when the value calculatedthrough equation (3) is maximized as the mechanical resonance frequencyand determines the mechanical resonance frequency as the operationfrequency reference value. Herein, ‘X’ is a stroke estimate value and‘i’ is a value of a current applied to the motor.

Thereafter, the controller 20 controls an operation of the compressor 60by varying a current operation frequency of the compressor 60 accordingto the operation frequency reference value outputted from the operationfrequency reference value determining unit 100. That is, if theoperation frequency reference value is greater than the currentoperation frequency value, the controller 20 increases the currentoperation frequency. If the operation frequency reference value issmaller than the current operation frequency value, the controller 20reduces the current operation frequency.

A stroke phase and a current phase of the compressor will be describedwith reference to FIG. 7.

FIG. 7 is a graph showing a phase of a current applied to a motor of thecompressor and a phase of a stroke of the compressor in accordance withthe second embodiment of the present invention. Namely, FIG. 7 shows aphase obtained by integrating the current phase of FIG. 4A and thestroke phase.

As shown in FIG. 7, experimentation reveals that even though the load ofthe compressor, when the sum of values obtained by multiplying thestroke estimate values and the integrated current values becomes themaximum, the resonance phenomenon occurs. That is, the integratedcurrent values and the stroke estimate values during one period aremultiplied when the motor is in the resonant state, and then when themultiplied values are added, the added value becomes the maximum.Accordingly, the operation frequency detected when the sum of valuesobtained by multiplying the integrated current values and the strokeestimate values becomes the maximum, is the same as the mechanicalresonance frequency.

The operation of the operation frequency reference value determiningunit 100 of multiplying the integrated stroke values and the currentvalues during one period, adding the multiplied values, detecting theoperation frequency when the sum is the maximum, and determining thedetected operation frequency value as an operation frequency referencevalue will be described with reference to FIG. 5 as follows.

FIG. 8 is a flow chart of a method for controlling an operation of thecompressor in accordance with the second embodiment of the presentinvention.

As shown in FIG. 8, a method for controlling an operation of thecompressor in accordance with the second embodiment of the presentinvention includes: detecting values of a current and voltage applied tothe compressor 60; calculating a stroke estimate value of the compressorbased on the current and voltage values; integrating the stroke estimatevalue to output an integrated stroke estimate value; detecting amechanical resonance frequency of the compressor based on the sum ofvalues obtained by multiplying the stroke estimate values and integratedcurrent values during one period and determining the mechanicalresonance frequency as an operation frequency reference value; andvarying a current operation frequency of the compressor according to thedetermined operation frequency reference value.

Herein, the operation frequency detected when the sum of values obtainedby multiplying the integrated stroke estimate values and the currentvalues during one period is the maximum is the same as the mechanicalresonance frequency of the compressor. Accordingly, when the currentoperation frequency of the compressor is varied according to theoperation frequency detected when the sum of values obtained bymultiplying the stroke estimate values and the integrated current valuesduring one period is the maximum, because the varied operation frequencyis the same as the mechanical resonance frequency, the operationefficiency of the compressor can be enhanced.

First, the operation frequency reference value determining unit 100multiples the stroke estimate values and the integrated current valuesduring one period, adds the multiplied values (step S21), and thencompares the calculated sum with the sum of values obtained bymultiplying stroke estimate values and integrated current values duringa previous one period (step S22).

If the sum of the values obtained by multiplying the stroke estimatevalues and the integrated current values during one period is greaterthan the sum of values obtained by multiplying the stroke estimatevalues and the integrated current values during a previous one periodand the current operation frequency of the compressor 60 is greater thana previous operation frequency (step S23), the operation frequencyreference value determining unit 100 continuously increases the currentoperation frequency, and then, determines an operation frequency (thesame as the mechanical resonance frequency) detected when the sum of thevalues obtained by multiplying the stroke estimate values and theintegrated current values during one period becomes the maximum, as anoperation frequency reference value (step S25).

If the sum of the values obtained by multiplying the stroke estimatevalues and the integrated current values during one period is greaterthan the sum of values obtained by multiplying the stroke estimatevalues and the integrated current values during a previous one periodand the current operation frequency of the compressor 60 is smaller thana previous operation frequency (step S23), the operation frequencyreference value determining unit 100 continuously reduces the currentoperation frequency, and then, determines an operation frequencydetected when the sum of the values obtained by multiplying the strokeestimate values and the integrated current values during a current oneperiod becomes the maximum, as an operation frequency reference value(step S26).

If the sum of the values obtained by multiplying the stroke estimatevalues and the integrated current values during one period is smallerthan the sum of values obtained by multiplying the stroke estimatevalues and the integrated current values during a previous one periodand the current operation frequency of the compressor 60 is smaller thana previous operation frequency (step S24), the operation frequencyreference value determining unit 100 continuously increases the currentoperation frequency, and then, determines an operation frequencydetected when the sum of the values obtained by multiplying the strokeestimate values and the integrated current values during a current oneperiod becomes the maximum, as an operation frequency reference value(step S27).

If the sum of the values obtained by multiplying the stroke estimatevalues and the integrated current values during one period is smallerthan the sum of values obtained by multiplying the stroke estimatevalues and the integrated current values during a previous one periodand the current operation frequency of the compressor 60 is greater thana previous operation frequency (step S24), the operation frequencyreference value determining unit 100 continuously reduces the currentoperation frequency, and then, determines an operation frequencydetected when the sum of the values obtained by multiplying the strokeestimate values and the integrated current values during a current oneperiod becomes the maximum, as an operation frequency reference value(step S28).

Accordingly, since the operation frequency detected when the sum ofvalues obtained by multiplying the stroke estimate values and theintegrated current values during one period becomes the maximum is thesame as the mechanical resonance frequency of the compressor, theoperation efficiency of the compressor can be enhanced by varying thecurrent operation frequency according to the operation frequencydetected when the sum of values obtained by multiplying the strokeestimate values and the integrated current values during one periodbecomes the maximum.

In other words, while the reciprocating compressor is operating,whenever a load of the compressor is varied, a mechanical resonancefrequency of the compressor is detected based on the stroke estimatevalues and the integrated current values during one period, and then,the operation frequency of the compressor is varied according to thedetected mechanical resonance frequency, thereby enhancing the operationefficiency of the compressor.

As so far described, the apparatus and method for controlling anoperation of a reciprocating compressor in accordance with the presentinvention have the following advantages.

That is, for example, whenever a load of the compressor is varied, amechanical resonance frequency of ht compressor is detected based onintegrated stroke values and current values during one period and anoperation frequency of the compressor is varied according to thedetected mechanical resonance frequency. Thus, even when the load of thecompressor is varied, the operation efficiency of the compressor can beenhanced.

In addition, whenever a load of the compressor is varied, a mechanicalresonance frequency of ht compressor is detected based on stroke valuesand integrated current values during one period and an operationfrequency of the compressor is varied according to the detectedmechanical resonance frequency. Thus, even when the load of thecompressor is varied, the operation efficiency of the compressor can bealso enhanced.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are therefore intendedto be embraced by the appended claims.

1. An apparatus for controlling a compressor comprising: a strokecalculator for calculating a stroke estimate value of a compressor basedon a value of a current applied to a motor of the compressor and a valueof a voltage applied to the motor of the compressor; an operationfrequency reference determining unit for integrating the stroke estimatevalue to output an integrated stroke value, detecting a mechanicalresonance frequency of the compressor based on the integrated strokeestimate value and the current value, and determining the detectedmechanical resonance frequency as an operation frequency referencevalue, wherein the operation frequency reference value determining unitmultiplies the integrated stroke values and current values during onetime period, and determines an operation frequency of the compressordetected when the sum of the multiplied values is 0 as the operationfrequency reference value; and a controller for varying a currentoperation frequency of the compressor according to the determinedoperation frequency reference value.
 2. The apparatus of claim 1,wherein the operation frequency detected when the sum of the multipliedvalues is 0 is identical to the mechanical resonance frequency of thecompressor.
 3. The apparatus of claim 1, wherein the operation frequencyreference value is an operation frequency value detected when a valuecalculated through equation Σ(∫Xdt×i) is 0, wherein ‘X’ is the strokeestimate value and ‘i’ is the value of the current applied to the motor.4. The apparatus of claim 1, wherein if a sum of the values obtained bymultiplying the integrated stroke values and the current values duringone time period is greater than a previous sum of values obtained bymultiplying the integrated stroke estimate values and the current valuesduring a previous one time period and the current operation frequency isgreater than a previous operation frequency, then the operationfrequency reference value determining unit continuously reduces thecurrent operation frequency, and then, determines the operationfrequency detected when the sum of the values obtained by multiplyingthe integrated stroke estimate values and the current values during acurrent one time period becomes 0, as the operation frequency referencevalue.
 5. The apparatus of claim 1, wherein if a sum of values obtainedby multiplying integrated stroke estimate values and the current valuesis greater than a previous sum of values obtained by multiplying theintegrated stroke estimate values and the current values during aprevious time period and the current operation frequency is smaller thana previous operation frequency, then the operation frequency referencevalue determining unit continuously increases the current operationfrequency, and then, determines the operation frequency detected whenthe sum of values obtained by multiplying the integrated stroke estimatevalues and the current values during the current one time period is 0 asthe operation frequency reference value.
 6. The apparatus of claim 1,wherein if a sum of values obtained by multiplying integrated strokeestimate values and the current values is smaller than a previous sum ofvalues obtained by multiplying the integrated stroke estimate values andthe current values during a previous time period and the currentoperation frequency is smaller than a previous operation frequency, thenthe operation frequency reference value determining unit continuouslyreduces the current operation frequency, and then, determines theoperation frequency detected when the sum of values obtained bymultiplying the integrated stroke estimate values and the current valuesduring the current one time period is 0 as the operation frequencyreference value.
 7. The apparatus of claim 1, wherein if a sum of valuesobtained by multiplying integrated stroke estimate values and thecurrent values is smaller than a previous sum of values obtained bymultiplying the integrated stroke estimate values and the current valuesduring a previous time period and the current operation frequency isgreater than a previous operation frequency, then the operationfrequency reference value determining unit continuously increases thecurrent operation frequency, and then, determines the operationfrequency detected when the sum of values obtained by multiplying theintegrated stroke estimate values and the current values during thecurrent one time period is 0 as the operation frequency reference value.8. An apparatus for controlling an operation of a compressor comprising:a current detector for detecting a current applied to a motor of thecompressor; a voltage detector for detecting a voltage applied to themotor; a stroke calculator for calculating a stroke estimate value ofthe compressor based on the detected current and voltage values and aparameter of the motor; an operation frequency reference valuedetermining unit for integrating the stroke estimate value to output anintegrated stroke value, detecting a mechanical resonance frequency ofthe compressor based on the integrated stroke estimate value and thedetected current value, and determining the detected mechanicalresonance frequency as an operation frequency reference value, whereinthe operation frequency reference value determining unit multiplies theintegrated stroke values and current values during one time period, anddetermines an operation frequency of the compressor detected when thesum of the multiplied values is 0 as the operation frequency referencevalue; a comparator for comparing the stroke estimate value outputtedfrom the stroke calculator with a stoke reference value and outputting adifference value according to the comparison result; and a controllerfor controlling an operation of the compressor by varying a currentoperation frequency according to the determined operation frequencyreference value and varying the voltage applied to the motor of thecompressor according to the difference value outputted from thecomparator.
 9. A method for controlling an operation of a compressorcomprising: integrating a stroke estimate value of the compressor basedon a value of a current applied to a motor of the compressor and avoltage applied to the motor and outputting an integrated stroke value;detecting a mechanical resonance frequency of the compressor based onthe integrated stroke estimate value and the current value; determiningthe mechanical resonance frequency as an operation frequency referencevalue of the compressor; and varying a current operation frequency of acompressor according to the determined operation frequency referencevalue, wherein the step of determining the mechanical resonancefrequency as an operation frequency reference value of the compressorcomprises multiplying the integrated stroke values and current valuesduring one time period, and determining an operation frequency of thecompressor detected when the sum of the multiplied values is 0 as theoperation frequency reference value.
 10. The method according to claim9, wherein the operation frequency reference value is an operationfrequency value detected when a value calculated through equationΣ(∫Xdt×i) is 0, wherein ‘X’ is the stroke estimate value and ‘i’ is thevalue of the current applied to the motor.
 11. The method of claim 9,wherein the step of determining the mechanical resonance frequency asthe operation frequency reference value comprises: a step in which if asum of the values obtained by multiplying the integrated stroke valuesand the current values during one time period is greater than a previoussum of values obtained by multiplying the integrated stroke estimatevalues and the current values during a previous one time period and thecurrent operation frequency of the compressor is greater than a previousoperation frequency, then the current operation frequency iscontinuously reduced and the operation frequency detected when the sumof the values obtained by multiplying the integrated stroke estimatevalues and the current values during a current one time period becomes0, is determined as the operation frequency reference value; a step inwhich if the sum of values obtained by multiplying integrated strokeestimate values and the current values is greater than the sum of valuesobtained by multiplying the integrated stroke estimate values and thecurrent values during the previous time period and the current operationfrequency is smaller than a previous operation frequency, the currentoperation frequency is continuously increased and the operationfrequency detected when the sum of values obtained by multiplying theintegrated stroke estimate values and the current values during thecurrent one time period is 0 is determined as the operation frequencyreference value; a step in which if the sum of values obtained bymultiplying integrated stroke estimate values and the current values issmaller than the sum of values obtained by multiplying the integratedstroke estimate values and the current values during the previous timeperiod and the current operation frequency is smaller than a previousoperation frequency, the current operation frequency is continuouslyreduced and the operation frequency detected when the sum of valuesobtained by multiplying the integrated stroke estimate values and thecurrent values during the current one time period is 0 is determined asthe operation frequency reference value; and a step in which if the sumof values obtained by multiplying integrated stroke estimate values andthe current values is smaller than the sum of values obtained bymultiplying the integrated stroke estimate values and the current valuesduring the previous time period and the current operation frequency isgreater than a previous operation frequency, the current operationfrequency is continuously increased and the operation frequency detectedwhen the sum of values obtained by multiplying the integrated strokeestimate values and the current values during the current one timeperiod is 0 is determined as the operation frequency reference value.12. An apparatus for controlling an operation of a compressorcomprising: a stroke calculator for calculating a stroke estimate valueof the compressor based on a value of a current applied to a motor ofthe compressor and a value of a voltage applied to the motor of thecompressor; an operation frequency reference value determining unit forintegrating the current value to output an integrated current value,detecting a mechanical resonance frequency of the compressor based onthe stroke estimate value and the integrated current value, anddetermining the detected mechanical resonance frequency as an operationfrequency reference value, wherein the operation frequency referencevalue determining unit multiplies the stroke estimate values andintegrated current values during one time period, and determines anoperation frequency of the compressor detected when the sum of themultiplied values becomes the maximum as the operation frequencyreference value; and a controller for varying a current operationfrequency of the compressor based on the determining the operationfrequency reference value.
 13. The apparatus of claim 12, wherein theoperation frequency detected when the sum of the multiplied values isthe maximum is identical to the mechanical resonance frequency of thecompressor.
 14. The apparatus of claim 12, wherein the operationfrequency reference value is an operation frequency value detected whena value calculated through equation Σ(X×∫idt) is the maximum, wherein‘X’ is the stroke estimate value and ‘i’ is the value of the currentapplied to the motor.
 15. The apparatus of claim 12, wherein if a sum ofthe values obtained by multiplying the stroke estimate values and theintegrated current values during one time period is greater than aprevious sum of values obtained by multiplying the stroke estimatevalues and the integrated current values during a previous one timeperiod and the current operation frequency of the compressor is greaterthan a previous operation frequency, then the operation frequencyreference value determining unit continuously increases the currentoperation frequency, and then, determines the operation frequencydetected when the sum of the values obtained by multiplying the strokeestimate values and the integrated current values during one time periodbecomes the maximum as the operation frequency reference value.
 16. Theapparatus of claim 12, wherein if a sum of the values obtained bymultiplying the stroke estimate values and the integrated current valuesduring one time period is greater than a previous sum of values obtainedby multiplying the stroke estimate values and the integrated currentvalues during a previous one time period and the current operationfrequency of the compressor is smaller than a previous operationfrequency, then the operation frequency reference value determining unitcontinuously reduces the current operation frequency, and then,determines the operation frequency detected when the sum of the valuesobtained by multiplying the stroke estimate values and the integratedcurrent values during a current one time period becomes the maximum asthe operation frequency reference value.
 17. The apparatus of claim 12,wherein if a sum of the values obtained by multiplying the strokeestimate values and the integrated current values during one time periodis smaller than a previous sum of values obtained by multiplying thestroke estimate values and the integrated current values during aprevious one time period and the current operation frequency of thecompressor is smaller than a previous operation frequency, then theoperation frequency reference value determining unit continuouslyincreases the current operation frequency, and then, determines theoperation frequency detected when the sum of the values obtained bymultiplying the stroke estimate values and the integrated current valuesduring a current one time period becomes the maximum as the operationfrequency reference value.
 18. The apparatus of claim 12, wherein if asum of the values obtained by multiplying the stroke estimate values andthe integrated current values during one time period is smaller than aprevious sum of values obtained by multiplying the stroke estimatevalues and the integrated current values during a previous one timeperiod and the current operation frequency of the compressor is greaterthan a previous operation frequency, then the operation frequencyreference value determining unit continuously reduces the currentoperation frequency, and then, determines the operation frequencydetected when the sum of the values obtained by multiplying the strokeestimate values and the integrated current values during a current onetime period becomes the maximum as the operation frequency referencevalue.
 19. An apparatus for controlling an operation of a compressorcomprising: a current detector for detecting a current applied to amotor of the compressor; a voltage detector for detecting a voltageapplied to the motor; a stroke calculator for calculating a strokeestimate value of the compressor based on the detected current andvoltage values and a parameter of the motor; an operation frequencyreference value determining unit for integrating the current value tooutput an integrated current value, detecting a mechanical resonancefrequency of the compressor based on the stroke estimate value and theintegrated current value, and determining the detected mechanicalresonance frequency as an operation frequency reference value, whereinthe operation frequency reference value determining unit multiplies thestroke estimate values and integrated current values during one timeperiod, and determines an operation frequency of the compressor detectedwhen the sum of the multiplied values becomes the maximum as theoperation frequency reference value; a comparator for comparing thestroke estimate value outputted from the stroke calculator with a strokereference value and outputting a difference value according to thecomparison result; and a controller for controlling an operation of thecompressor by varying a current operation frequency according to thedetermined operation frequency reference value and varying the voltageapplied to the motor of the compressor according to the difference valueoutputted from the comparator.
 20. A method for controlling an operationof a compressor comprising: calculating a stroke estimate value of thecompressor based on a value of a current applied to a motor of thecompressor and a value of a voltage applied to the motor; integratingthe current value to output an integrated current value; detecting amechanical resonance frequency of the compressor based on the strokeestimate value and the integrated current value; and determining themechanical resonance frequency as an operation frequency reference valueof the compressor; and varying a current operation frequency of thecompressor according to the determined operation frequency referencevalue, wherein the step of determining the mechanical resonancefrequency as an operation frequency reference value of the compressorcomprises multiplying the stroke estimate values and integrated currentvalues during one time period, and determining an operation frequency ofthe compressor detected when the sum of the multiplied values becomesthe maximum as the operation frequency reference value.
 21. The methodof claim 20, wherein the step of determining the mechanical resonancefrequency as the operation frequency reference value comprises: a stepin which if a sum of the values obtained by multiplying the strokeestimate values and the integrated current values during one time periodis greater than a previous sum of values obtained by multiplying thestroke estimate values and the integrated current values during aprevious one time period and the current operation frequency of thecompressor is greater than a previous operation frequency, then thecurrent operation frequency is continuously increased and the operationfrequency detected when the sum of the values obtained by multiplyingthe stroke estimate values and the integrated current values during onetime period becomes the maximum is determined as the operation frequencyreference value; a step in which if the sum of the values obtained bymultiplying the stroke estimate values and the integrated current valuesduring one time period is greater than the sum of values obtained bymultiplying the stroke estimate values and the integrated current valuesduring a previous one time period and the current operation frequency ofthe compressor is smaller than a previous operation frequency, then thecurrent operation frequency is continuously reduced and the operationfrequency detected when the sum of the values obtained by multiplyingthe stroke estimate values and the integrated current values during acurrent one time period becomes the maximum is determined as theoperation frequency reference value; a step in which if the sum of thevalues obtained by multiplying the stroke estimate values and theintegrated current values during one time period is smaller than the sumof values obtained by multiplying the stroke estimate values and theintegrated current values during a previous one time period and thecurrent operation frequency of the compressor is smaller than a previousoperation frequency, then the current operation frequency iscontinuously increased and the operation frequency detected when the sumof the values obtained by multiplying the stroke estimate values and theintegrated current values during a current one time period becomes themaximum is determined as the operation frequency reference value; and astep in which if the sum of the values obtained by multiplying thestroke estimate values and the integrated current values during one timeperiod is smaller than the sum of values obtained by multiplying thestroke estimate values and the integrated current values during aprevious one time period and the current operation frequency of thecompressor is greater than a previous operation frequency, then thecurrent operation frequency is continuously reduced and the operationfrequency detected when the sum of the values obtained by multiplyingthe stroke estimate values and the integrated current values during acurrent one time period becomes the maximum is determined as theoperation frequency reference value.